In recent years, as diversification of people's life patterns progresses, advertisements have considerable influences on people. In this connection, as railroads are used by many people on a daily basis, advertisements such as displaying in train vehicles have significant effects, and thus the demand for advertisements in train vehicles is rapidly increasing. With a view to such demand, in recent years, there has been provided a service in which a display medium such as an LCD display is installed on a panel portion above doors in a train vehicle and train operation information such as the destination, stopping stations, travelling position, and delay information, as well as image contents of video images or still images (such as advertisements and news) are distributed by the display medium. In the following descriptions, the system of distributing image contents in a vehicle is referred to as “in-vehicle information distribution system”.
In the in-vehicle information distribution system, image contents are generally distributed by the following three methods. In a first method, a central device installed near a train driver's seat is connected to a terminal (a modem) installed in each vehicle through an analog line, image data of image contents is transmitted via the central device and the modem to an image display device in each vehicle, and images such as advertisements and news are displayed on the image display device. The first method has a problem that the image quality is degraded.
In a second method, a central device is digitally connected to an image display device through Ethernet® and the like, image data is distributed by broadcast and decoded in each image display device, and then images are displayed on each image display device. While this method can provide clear images, similarly to the first method, the second method assumes that the same image contents are displayed on all the image display devices. While it is technically possible to distribute different image data to respective image display devices, it is not realistic because the band of an in-vehicle communication path is limited in a particular environment such as a train vehicle.
In a third method, similarly to the second method, a central device is digitally connected to an image display device, image contents are transmitted in advance from the central device to each image display image, and the image contents are accumulated in each image display device and displayed. According to this method, it is possible to transmit different image contents to respective image display devices, and thus problems of the two methods explained above can be solved. Hereinafter, this method is referred to as “image-display-device accumulation type”.
In a conventional technique described in Patent Literature 1 as an example of the device of the image-display-device accumulation type, contents data is stored in a contents display device (corresponding to “image display device”), streaming data is stored in a management server (corresponding to “central device”) that manages an image, and these pieces of data are displayed according to switching control.